Parameters affecting the properties of dynamic membranes formed by Zr hydroxide colloids

Membranes exhibiting separation properties similar to those of conventional UF membranes can be dynamically prepared on a porous substrate by in-situ deposition of particles from a circulating colloidal suspension of certain hydrous oxides, notably Zr hydroxide, The objective of this work is to eluc idate parameters affecting Zr hydroxide colloidal properties in order to de termine optimal conditions for dynamic membrane (DM) formation on substrate s of different porosity, The main parameters studied were the effects of pH , Zr concentration and ionic strength on colloidal properties, The main res ults were as follows. Over the pH range from 3 to 4, a stable mono-disperse colloidal dispersion was obtained, composed of sub-micron particles. The p article size increased systematically with the pH level of the suspension, At a pH value of near 4, a bi-modal distribution was obtained, composed of both sub-micron particles and very large agglomerates. At pH values higher than about 4.5, large agglomerates formed instantly Particle agglomeration was also affected by the ionic strength of the solution and the procedure o f the colloid preparation. The above results find full support in the flow and separation properties displayed by DM prepared with Zr suspensions of d ifferent chemistries (notably the pH level) on two types of substrate: a po rous fabric having a pore size of tens of microns and a microfiltration mem brane having a pore size of a few microns.